PRL Article Demonstrates Potential for Ultra-Stable Laser-Cooled Clocks

This week an article in the Physical Review Letters by Chad Fertig and Kurt Gibble of Yale University reports a measurement of the cold collision frequency shift in a 87Rb clock. The authors find the frequency shift in 87Rb caused by the cold collisions to be 30 times smaller than the shift for cesium atoms. For 87Rb the shift is much smaller due to the absence of resonances, and because of a remarkable near-equality of scattering lengths. The authors also demonstrated a further reduction of the small shift by detuning the clock cavity to cancel the collision shift, a trick used in hydrogen masers (spin exchange tuning). This cancellation of the small frequency shift may allow rubidium fountain clocks to have a high short-term stability and accuracy exceeding 1 part in 1016. Gibble is the Principal Investigator for the flight experiment RACE (Rubidium Atomic Clock Experiment), which will compare high-accuracy rubidium clocks on the ISS and Earth, demonstrating new clock techniques and testing relativity. Chad Fertig is a GSRP fellow.